The present invention relates to a method and a device for detecting an engine speed signal.
With modern internal-combustion engines, the rotational-speed signal delivers information of key importance to engine management, diagnosis and optimization with regard for various criteria. According to the related art, engine speed is measured with the aid of a sensing wheel mounted on the crankshaft, the sensing wheel having a certain number of markings. The individual markings or increments are detected by a sensor.
The sensing wheels typically have tolerance-related geometric errors and installation faults. These faults cause a systematic error that substantially degrades the continued use of the rotational-speed signal and, in some circumstances, even renders it unusable for certain functionalities. It is therefore crucial that these faults be identified and compensated for.
A number of methods are known in this context:
A method is known from DE 100 17 107 A1 with which the sensing wheel errors—except for the frequency components of the main orders of the engine—can be compensated for. The method is based on the fact that the rotational non-uniformity of the internal-combustion engine only has the frequency components mentioned previously. They are estimated and removed from the rotational-speed signal. The remaining fluctuations are attributed to the effects of the sensing wheel errors.
In DE 197 33 958 A1 and WO 01/77692, a segment-based correction of the rotational-speed signal is carried out with low angular resolution.
In DE 101 07 892 A1, the rotational non-uniformities are estimated, using models, based on the intake-manifold pressure, ambient pressure, engine geometry and control times, and they are used, together with the measured rotational-speed signal, to calculate the individual sensing wheel errors.
The method described in WO 03/062620 assumes that the moments of inertia and engine gas acting on the shaft cancel each other out statistically, at least to a great extent, when the averaging process is carried out within a certain rotational speed range. Based on the mean profile of angular speed calculated in this manner, the geometric errors of the sensing wheel are identified.
With modern systems for gasoline and diesel engines, access to the fuel and air path is enabled on a cylinder-specific basis. To fully utilize the potential available to reduce fuel consumption and emissions, the engine management system must receive feedback on the processes that are actually taking place in the combustion chamber. The course of pressure in the combustion chamber over time is a key quantity used to realize functionalities of cylinder-specific engine management and control. Even when a series-production combustion chamber pressure sensor does become available, it is not always possible to indicate all cylinders in an engine, due to reasons of cost and limitations on installation space.